>>121587703I also consider the vocals to have a distinctively closer to prog quality than most of their contemporaries, and the bass on Still... is definitely also a prog element as it puts an emphasis on technical skill and the composition as a whole is more technical than the majority of popular ballad style songs of 1973.
I completely understand why someone else might exclude those songs from their particular definition of the genre, but I personally don't think a particularly strict or specific definition is constructive or even sufficient, because the only way to do that would be to split it into chronological subcategories which, again, don't have very much in common aside from the people who are making the music.